Find enough advanced weaponry to get past a Spider Mastermind and exit the level. Be careful not to wake him up sooner than you need to. The start of the map is a scramble for survival. I recommend heading up to the Mancubus's platform, grabbing the the Super Shotgun and box of shells, and you should be alright.

Also, after teleporting into a tower, the idea is to grab the Rocket Launcher and jump out the window. If you go too close to the window you will trigger something very dangerous, so stay away until you are sure you want to leave.